This project is investigating calcium metabolism during pregnancy and the perinatal period in humans and non-human primates. The basic experimental design involves measurement of parathyroid hormones, calcitonin, total and ionic calcium, magnesium, phosphorus, and albumin in serum or plasma samples under a variety of conditions. In humans, studies are being done longitudinally throughout normal pregnancy as well as in a variety of pregnancy complications. At the time of birth, cord blood is collected and analyzed for comparison with the neonatal serum calcium level at 24 hours. In Rhesus monkeys in late pregnancy, the response of the fetus is being examined by assessing PTH response to EDTA-induced hypocalcemia and CT response to hypercalcemia. Monkey studies are done at differing gestational ages. Results of the study thus far indicate that the principal maternal physiologic adjustment is an increase in PTH secretion, maintaining the serum ionized calcium level within the normally narrow physiologic limits. In monkeys, the fetus seems quite capable of response to provocative stimuli by releasing calcium regulating hormones.